This section provides background information related to the present disclosure which is not necessarily prior art.
High-energy density electrochemical cells, like lithium ion batteries, can be used in a variety of applications, including for consumer products, like electronics, power tools, lawn and garden equipment, motorized wheelchairs, toys, and for transportation. An exemplary use in transportation includes vehicles, such as Hybrid Electric Vehicles (HEVs) and Electric Vehicles (EVs). Typical lithium ion batteries comprise a first electrode (e.g., a positive electrode or cathode), a second electrode (e.g., a negative electrode or anode), an electrolyte material, and a separator. Often a stack of lithium ion battery cells is electrically connected to increase overall output. Conventional lithium ion batteries operate by reversibly passing lithium ions between the negative electrode and the positive electrode. A separator and an electrolyte are disposed between the negative and positive electrodes. The electrolyte is suitable for conducting lithium ions and may be in solid or liquid form. Lithium ions move from a cathode (positive electrode) to an anode (negative electrode) during charging of the battery, and in the opposite direction when discharging the battery. For convenience, a negative electrode will be used synonymously with an anode, although as recognized by those of skill in the art, during certain phases of lithium ion cycling, the anode function may be associated with the positive electrode rather than the negative electrode (e.g., the negative electrode may be an anode on discharge and a cathode on charge). Likewise, a positive electrode will be used synonymously with a cathode, although the same is true.
Contact of the anode and cathode materials with the electrolyte can create an electrical potential between the electrodes. When electron current is generated in an external circuit between the electrodes, the potential is sustained by electrochemical reactions within the cells of the battery. Each of the negative and positive electrodes within a stack is connected to a current collector (formed of a metal, such as copper or nickel for the anode and aluminum for the cathode). The stack also has a first and second terminal end plate that is disposed adjacent to a terminal electrode on each terminal end. Each current collector within the stack typically has an electrically conductive tab that extends therefrom. Where there are multiple positive and negative current collectors in a stack, the positive current collector tabs are connected together in parallel and the negative current collector tabs are likewise connected together in parallel. The plurality of tabs is typically welded together, for example, by ultrasonic welding. During battery usage, the current collectors associated with each electrode are connected by an external circuit that allows current generated by electrons to pass between the electrodes to compensate for transport of lithium ions. However, over time, the welded current collector tabs can be weakened through thermal or volumetric cycling during battery use.
Thus, it would be desirable to enhance the robustness of a stack of battery cells for long-term use by potentially eliminating multiple current collector tabs for each current collector. Further, it would be desirable to increase the specific energy and energy density (charge capacity per unit volume and mass) of the battery, such as high power lithium ion batteries, by reducing the weight of various current collector components and improving battery performance.